A Chinese court has sentenced two Tibetan monks to long prison terms Tuesday in an unusual case that has prompted widespread international attention.

The United States expressed concern over the 11-year term given another monk Monday. All three monks are accused of contributing to the death of 16-year-old Rigzin Phuntsog, who burned himself to death in March at the Kirti monastery in southwestern Sichuan province.

The court Tuesday sentenced Tsering Tenzin to 13 years in prison and Tenchum, who uses only one name, to 10 years. Both were accused of instigating and assisting in Phuntsog's death.

The official Xinhua news agency said the court was shown evidence that the monks had sent photos of Phuntsog outside of China days before the self-immolation, indicating that it was pre-meditated. It said the monks admitted their guilt after the proceedings.

On Monday, the court convicted a monk named Drongdru for having hidden the severely injured Phuntsog for 11 hours, preventing him from receiving medical treatment. Tibetan exile groups say Drongdru hid the young monk to protect him from police who began beating him after extinguishing the flames.

The U.S. State Department said Tuesday it was unclear whether Drongdru was accorded the legal rights to which he is entitled under the Chinese constitution. A spokesman urged China to ensure transparency and uphold the protections to which Chinese citizens are entitled.

Chinese authorities imposed a heavy security presence around the monastery following the immolation, which was reportedly carried out to protest Chinese restrictions on Tibetan religious practices. In June, the government explained the disappearance of more than 300 monks from the monastery by saying they were undergoing “legal education.”